1. Field of the Invention
The present invention relates to a method of manufacturing a ceramic film to be used in a piezoelectric actuator and an ultrasonic transducer, etc., and further relates to a structure including the ceramic film.
2. Description of a Related Art
A structure in which electrodes are formed on both sides of a piezoelectric material is utilized in various applications such as a piezoelectric actuator, a piezoelectric pump, an inkjet printer head, or an ultrasonic transducer. In recent years, with the developments of MEMS (micro electromechanical systems) related devices, elements having such multilayered structure shave been microfabricated still further and packaged more densely. Accordingly, microfabrication and improvement in performance are desired for the piezoelectric material to be used therein.
Under the circumstances, recent years, in order to form a piezoelectric material layer without mixing a binder, film formation methods utilizing a collision and deposition phenomenon of solid particles, such as an aerosol deposition (AD) method, a gas deposition method and so on, have attracted attention. For example, the AD method is a method of depositing a raw material on a substrate by injecting an aerosol formed by dispersing fine particles of the raw material in a gas from a nozzle toward the substrate and allowing the fine particles to collide against the substrate or a previously formed film. According to the AD method, a dense and strong thick film can be formed.
Further, Japanese Patent Application Publication JP-A-4-188503 discloses a method of manufacturing a ceramic dielectric product by forming a ceramic dielectric thick film layer having a thickness of 1 μm to 20 μm by suspending ceramic dielectric material fine particles having particle diameters of 1 μpm or less in a gas to form an aerosol and injecting the aerosol of ceramic dielectric material fine particles on a substrate via a nozzle at a high speed to deposit the particles thereon (page 1, FIG. 2).
Further, Japanese Patent Application Publication JP-P2004-43893A discloses a method of forming a ceramic film by spraying an aerosol containing ceramic powder on a substrate to grow a film on the substrate and allowing the ceramic powder to collide against the substrate in order to form a ceramic film with high crystallinity, wherein ceramic film formation is performed by employing ceramic powder having such high crystallinity that the half maximum full-width of the greatest intensity diffraction line peak of an X-ray diffraction line when using Cu—Kα ray is less than 0.3° (page 1, FIG. 1). That is, JP-P2004-43893A describes that it is important to make the crystallinity of the raw material powder higher in order to improve crystallinity of a ceramic film.
By the way, generally, the piezoelectric performance in a piezoelectric material largely depends on the degree of crystal orientation (rate of orientation). That is, the higher the degree of crystal orientation, the easier the alignment of polarization orientation when polarizing treatment is performed on the piezoelectric material, and good piezoelectric performance can be obtained. Here, the degree of orientation refers to a rate of crystal faces oriented toward a specific direction among crystal faces contained in a polycrystalline body. For example, the degree of orientation F(%) in c-axis is defined by the following equation.F(%)=(P−P0)/(1−P0)×100  (1)
In the equation (1), P0 is X-ray diffraction intensity in c-axis of a completely randomly oriented polycrystalline body, i.e., a ratio {ΣI0(0 0 L)/ΣI0(H K L)} of a total ΣI0(0 0 L) of reflection intensity I0(0 0 L) from a face (0 0 L) of the completely randomly oriented polycrystalline body to a total ΣI0(H K L) of reflection intensity I0(H K L) from the respective faces (H K L) of the polycrystalline body. Further, in the equation (1), P is X-ray diffraction intensity in c-axis of a sample, i.e., a ratio {ΣI(0 0 L)/ΣI(H K L)} of a total ΣI(0 0 L) of reflection intensity I(0 0 L) from a face (0 0 L) of the sample to a total ΣI(H K L) of reflection intensity I(H K L) from the respective faces (H K L) of the sample. Each of H, K, and L takes an arbitrary integer number equal to “0” or more.
Here, in the equation (1), P0 is a known constant. Therefore, in the case where the total ΣI (0 0 L) of reflection intensity I(0 0 L) from a face (0 0 L) and the total ΣI(H K L) of reflection intensity I(H K L) from the respective faces (H K L) are equal, that is, the degree of orientation F(%) in c-axis of the sample becomes 100%.
For example, in PZT (Pb(lead) zirconate titanate) as a representative piezoelectric material, the largest piezoelectric displacement is obtained when oriented in <0 0 1> direction in the tetragonal system, while the largest piezoelectric displacement is obtained when oriented in <1 1 1> direction in the rhombohedral system. Contrary, in a polycrystalline body with uncontrolled orientation, the crystal axis is randomly oriented, and therefore, the piezoelectric performance is inferior to that of the single-crystal body or polycrystalline body with controlled orientation. Accordingly, it is desired that the crystallinity can be made higher in the polycrystalline body for increasing the piezoelectric performance and the orientation can be controlled for increasing the degree of orientation.
However, according to the above-mentioned AD method, although a strong film with high adhesion can be formed, high heat treatment temperature is required for improving the crystallinity. Practically, the crystallinity and the piezoelectric performance of the PZT film are improved by annealing (heat-treatment) at high temperature near 1000° C. after film formation. Further, the orientation of the crystal faces is not controlled in the AD method. Accordingly, although the film formation itself by the AD method can be performed at temperature up to a ceiling of about 600° C., it is necessary to provide high energy to the film in a high-temperature process or the like in order to obtain sufficient piezoelectric performance for practical use.